Stabilized containment facility liner

ABSTRACT

The invention relates to a stabilized fluid barrier member and to methods of forming the same. The fluid barrier comprises a first outer sheet member having a top surface and a bottom surface, with a stabilizer element overlying at least part of the first sheet member top surface and abutting the top surface along at least a portion thereof. The stabilizer element contains a plurality of interstitial apertures adapted to contain a quantity of a selectively fluid-impervient barrier material and for substantially preventing displacement of the barrier material from the apertures, notwithstanding the angular inclination at which the fluid barrier member is oriented during manufacture, transport, installation and/or use. The barrier material is chosen for its ability to prevent passage of one or more particular fluids, in liquid or gas form, depending upon the application for which the barrier member is intended. The fluid barrier member of the invention may further comprise an optional second outer sheet member also having a top surface and a bottom surface. The second sheet member overlays at least part of the stabilizer element such that at least a portion of the second sheet member bottom surface abuts the stabilizer element. After positioning the various components of the barrier member in abutting stacked relation, they may all be bonded together along at least a portion of their abutting surfaces to form an interconnected laminate wherein the stabilizer element is in contact with and bonded to both the first and the second outer sheet members.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.08/299,778 filed Sep. 1, 1994, now U.S. Pat. No. 5,501,753.

TECHNICAL FIELD

The invention generally relates to an internally stabilized fluidbarrier member adapted for installation at any desired angularinclination without substantial shifting of one or more selectivelyfluid-impervient materials contained therein. In a preferred embodimentthe invention relates to a geosynthetic clay liner for use, e.g., inwaste containment facilities containing hazardous and/or municipal solidwaste, for preventing leachate therefrom from leaving the facility andpassing into adjacent groundwater systems.

Background of the Invention

As described herein, the fluid barrier of the invention is adaptable foruse in a variety of applications to prevent passage of selected"fluids", defined herein to include both liquids and gasses, between afirst location and a second location a distance removed therefrom byinterposing the barrier therebetween. One preferred use for the barriermember of the invention is as a geosynthetic clay liner for use inisolating leachate from a waste containment facility, e.g., a landfill,from adjacent groundwater systems. The applicability of the invention isnot, however, limited solely to use in waste containment facilities.Rather, the presently described fluid barrier member is useful in anysituation where it is desirable to selectively hinder or prevent theflow of one or more fluids from a first location to a second location adistance removed therefrom, particularly wherein the intervening surfacebetween the first and second locations is sloped or otherwise uneven.Such applications include, but are not limited to stabilizing thesubsurface soil supporting a roadway or a railroad track, constructing awater retaining structure such as an earthen dam or a canal, containingleakage from a pipeline, liquid containment facility, or storage tank,minimizing leakage into underground structures such as tunnels, mines,or retaining structures, insulating structures from hot or cold weatheror subsurface water attributable to the ground-water table or capillarymigration, and isolating the subterranean portion of buildings likely tobe affected by seismic forces. For convenience in explaining theinvention however, it will be mainly described herein with relation toits use as a waste containment facility liner or cover system with theunderstanding that such use is not limiting.

Waste containment facilities, such as landfills, are ordinarily providedwith a low hydraulic conductivity barrier and drainage system comprisinga liner formed of compacted clay or a layer of water swellable clayoverlain by one or more sheets of geosynthetic material, e.g., ageomembrane and a geotextile. Such liners are typically installed toisolate the leachate produced by the waste containment facility fromadjacent groundwater systems. In addition, these facilities are alsorequired to be covered with a low hydraulic conductivity barrier anddrainage system upon closure. In the United States liners and coversare, in fact, required for use in all hazardous waste and new orexpanded municipal solid waste containment facilities under subtitles Cand D of the Federal Resource and Conservation Recovery Act (1976).

The static and dynamic (e.g., seismic activity) stability of such linerand cover systems is controlled by their shear strength, as measured atthe component mid-plane or interfaces. Liner stability is of criticalimportance for preventing liner failure and release of leachate,particularly when the topographical surface of the waste containmentfacility site is not substantially level, i.e., wherein the surface ofthe facility slopes at a relatively substantial angle, i.e., of greaterthan about 9-10 degrees. Cover stability is also of critical importancefor preventing a slope stability failure that may endanger people orproperty and allow precipitation to infiltrate the waste.

In the earliest prior art, waste containment facility liners were formedby applying several feet of barrier material, such as natural soil or amixture of natural soil and bentonite, directly to the soil surface ofthe facility. The barrier material was thereafter impacted into placeand covered by a layer of soil. Thereafter however, a composite linerwas developed. These articles comprise a compacted clay liner overlainby a geomembrane. This dual component liner system was found to beuseful for providing multiple protection against leakage of leachatefrom waste containment facilities.

There are several major problems associated with the placement and useof the compacted clay liners described above. These include thedifficulty and expense of locating and transporting a suitable type andquantity of "borrow material", i.e., a term used in the art to describesoil which is used to construct the compacted clay layer in forming theliquid barrier; desiccation cracking in arid climates, freeze-thawcracking in cold climates and saturation or excessive water content inhumid climates. In addition, extremely expensive field test sections andfield hydraulic conductivity tests must be conducted to verify that thehydraulic conductivity is within the limits required under theapplicable regulations, i.e., hydraulic conductivity less than 10⁻⁷cm/second. The liner thus produced ranges up to about 3 feet inthickness and costs from about $3 to $10 per square foot to manufacture.

As noted above the compacted clay must, under the applicableregulations, exhibit a hydraulic conductivity of less than 10⁻⁷cm/second. The hydraulic conductivity of the compacted clay is, however,extremely sensitive to a number of liner construction parameters,including but not limited to the compaction water content, dry unitweight, the type of compaction equipment Used, compactive effort andnumber of compactor passes.

In general, however, increasing the compaction water content leads to adiminution in the hydraulic conductivity of the barrier, as well as thestrength of the interface between the compacted clay and thegeomembrane. Therefore, a compromise between minimizing the hydraulicconductivity versus maximizing the interface strength or stability issought. This requires, however, that during its construction, the linermust be limited to a narrow range of compaction water content and dryunit weight. This range is extremely difficult and expensive to achieveand maintain. The problems associated with compacted clay liners aresimilar to those associated with compacted clay covers.

In an effort to overcome the drawbacks described above with compactedclay liners and covers, prefabricated geosynthetic clay liners, e.g.,bentonite mats, prefabricated clay bentonite panels, clay mats, etc.("GCLs") were developed. GCLs generally fall into two main categories.In the first category a water-swellable colloidal clay, e.g., bentonite,is sandwiched between two geotextiles (examples of such products includeBentofix® manufactured by Naue Fasertechnik/Albarrie-Naue, Ltd anddistributed by National Seal Co., Aurora, Ill., Bentomat® by ColloidEnvironmental Technologies, Co., Arlington Heights, Ill, NaBento®manufactured by Huesker, Inc. of Charlotte, N.C. and Claymax® by theJames Clem Corp., Fairmont, Ga.). In the second category of GCLs,bentonite is mixed with an adhesive and glued to a geomembrane (anexample of such a product is Gundseal® produced by GSE LiningTechnology, Inc., Houston Tex.). Additional GCL manufacturers includeEnvironmental Protection Systems of Houston, Tex. and EnvironmentalProtection, Inc. of Mancelona, Mich.

GCLs contain approximately 5 kg/m² (1 lb./ft²) of bentonite and aremanufactured in panels with widths of approximately 2 to 3 meters andlengths of 25 to 60 meters. The panels are placed on rolls at thefactory where they are stored until shipped to the waste containmentfacility site where they are unrolled and installed in their finallocation. Their cost is substantially lower than that of compacted clayliners, i.e., thirty to sixty cents per square foot versus $3-10 persquare foot for the compacted clay liners.

Although GCLs are less expensive and easier to install (due to theirreduced bulk and prefabricated construction) than the compacted clayliners, they nevertheless also exhibit significant disadvantages. Asnoted above, the clay used in GCLs is typically bentonite, whichexhibits a hydraulic conductivity of less than 10⁻⁷ cm/sec., but onlywhen hydrated. Unhydrated bentonite, on the other hand, exhibits ahydraulic conductivity that is greater than the required value of 10⁻⁷cm/sec. Thus, hydration is required to maintain impermeability butleads, as discussed below, to a loss of internal and interface (e.g.,between two adjacent geosynthetics) strength, rendering such productsparticularly susceptible to damage due to shear caused, for example, byinstallation upon uneven (i.e., sloped) surfaces.

Further to the above, a significant disadvantage of GCLs is their lowinternal strength, i.e., at the interface between the bentonite and thegeotextile or geomembrane, resulting from the hydration of thebentonite, which is of particular importance in areas prone to seismicactivity. The peak and residual shear strength of hydrated bentonitecorrespond to a slope stability of 8 and 5 degrees, respectively. Thus,a hydrated bentonite GCL which is installed on ground having a slopegreater than about 5-8 degrees will not be stable. Therefore, such priorart GCLs are susceptible to shear damage caused by sliding through,i.e., within, the internal bentonite filling. Prior art GCLs are alsosusceptible to shear damage caused by sliding at the top or bottom ofthe product because hydrated bentonite extrudes through the geotextile,causing a reduction in interface strength between adjacentgeosynthetics.

Typical waste containment facility slopes range, however, from about 14to about 26 degrees, with some proposed slopes of about 90 degrees. Thusstatic and seismic instability is a serious consideration in GCLsutilized in such applications once the bentonite hydrates. As a result,modifications, i.e., by the addition of one or more geomembranesemplaced above and/or below the GCL, are required to decrease andpreferably prevent hydration. However, this creates additionalinterfaces, e.g., geomembrane/bentonite, along which shear failure canoccur. The earliest GCL products were known simply as GCLs since theyconsisted merely of a layer of bentonite sandwiched between twogeotextiles. Subsequently, to increase the shear resistance of thebentonite, manufacturers began using vertical needle punched fibers tosew the geotextiles together in order to confine and strengthen thebentonite. This method is used in the Bentofix® and Bentomat® productsmarketed, respectively, by National Seal Company and ColloidEnvironmental Technologies Company. Another method known in the art isto stitch bond the geotextiles together. This method is used in theClaymax® and NaBento® products marketed by James Clem Corporation andHuesker, Inc., respectively. Such needle punched and stitched productsare known as strengthened or improved GCLs. The vertical needle punchingand stitch bonding also provides some additional shearing resistance inthe middle of the GCL in an effort to prevent internal failure of thebentonite.

The strengthened construction described above suffers, however, from atleast one significant drawback in that the vertical needle punchingtends to tear or pull out due to small shear displacements (e.g., causedby shearing of the bentonite within the GCL), unconfined swelling of thebentonite, which may result in internal failure, (i.e., failure throughthe bentonite), or shear displacement along the upper or lower interfaceof the strengthened GCL. It has also been demonstrated that thestitching tends to act as a wick, thus increasing the permeability ofthe product. The shear displacement required to tear or pull out thevertical stitching is less than one inch, which can occur during use ofsuch products in the field. Thus, strengthened GCLs provide only aminimal increase in internal strength over earlier GCLs known and usedin the art. In fact, it has been demonstrated that the long-terminternal strength in a strengthened GCL is approximately equal to theshear strength of bentonite alone due to the vertical stitching tearingor pulling out of the geotextiles under sustained shear stress.

For all the reasons set forth above, there has been a long felt need bythose working in this field for a fluid barrier member which is stablewhen installed at inclinations greater than 5-8 degrees and which willnot undergo internal failure upon hydration. As explained below, thestabilized fluid barrier member of the present invention meets all ofthese criteria.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide astabilized fluid barrier member which is adapted to selectively preventthe passage of a variety of fluids from a first location, through thebarrier, to a second location. A quantity of one or more selectivelyfluid-impermeable materials, i.e., chosen according to the particularfluid which is intended to be prevented from passage through thebarrier, is contained within a stabilizer element located within themember. The stabilizer element is adapted to prevent displacement of thematerial(s) within the barrier member, notwithstanding the angularinclination at which the member is oriented during manufacture,transport, installation and/or use as well as to enhance bondingstrength among the various components of the barrier member, and toincrease tensile and internal shear strength of the product.

In a first embodiment, the invention relates to a stabilized fluidbarrier member comprising at least a first outer sheet member having atop surface and a bottom surface. The fluid barrier member furthercomprises a stabilizer element overlying at least part of the firstsheet member top surface and which abuts the top surface along at leasta portion thereof. The stabilizer element contains a plurality ofinterstitial apertures adapted to hold at least one selectivelyfluid-impervient barrier material and for substantially preventingdisplacement of the barrier material from the apertures, notwithstandingthe angular inclination at which the fluid barrier member is oriented.As indicated above, two or more different selectively fluid-impervientbarrier materials may be placed, if desired, within the apertures in thestabilizer element, either separately or in admixture.

Barrier materials for use in the invention may, for example, be selectedfrom among man-made materials such as the so-called "superabsorbent"polymer resin materials and naturally occurring materials such as sand,starch, e.g., corn starch and the water swellable colloidal clays, whichare well known in the art. The invention is not limited to the use ofthese particular materials however, as substantially any barriermaterial having the intended effect, i.e., selectively blocking passageof one or more fluids, may be used in the invention. Such materials arecommonly available in the marketplace and their identity would bereadily apparent to those working in the field to which the invention isto be applied.

The phrase "selectively fluid-impermeable" as used herein means that thematerial chosen for use in a particular application is chosen accordingto its ability to prevent passage of one or more selected fluids (i.e.,a liquid and/or a gas as that term is used herein) between a firstlocation on one side of the barrier member and a second location on theother side thereof. That is, the fluid barrier material is not the samein every instance, nor is the invention limited to the use of just onesuch material at a time. Rather, the fluid-impervient material, orcombination of materials, is chosen with the specific intent ofpreventing passage of one or more particular fluids through the barriermember, depending upon the intended application. One of ordinary skillin the art would readily be able to select the most useful barriermaterial(s) for preventing passage of a particular fluid without theneed for undue experimentation since the properties of various barriermaterials are well known in the art.

The fluid barrier member of the invention may, if desired, furthercomprise an (optional) second outer sheet member, also having a topsurface and a bottom surface. When it is included, the second sheetmember overlays at least a portion of the stabilizer element such thatat least a portion of the second sheet member bottom surface abuts theotherwise uncovered surface of the stabilizer element. When the secondmember is not included, the barrier material may be retained within thestabilizer element using an appropriate mechanism such as an adhesive.In an alternate embodiment, the barrier material can be placed on asurface in the field and a unitary construct comprising a stabilizerelement and top sheet member placed over it in a manner so as tosubstantially fill the apertures in the stabilizer element. Thisembodiment does not include a second sheet member.

In one embodiment of the invention, the first and/or second outer sheetmembers are formed of a geotextile. The most preferred geotextile isnon-woven polyester. In an alternate embodiment of the invention, thefirst and/or second outer sheet members are geomembranes. A preferredgeomembrane for use with the invention is polyethylene. Both the lowerand optional upper (when included) sheet members need not be formed ofidentical materials.

Once the various components of the fluid barrier member of the inventionare positioned in abutting stacked relation, they are preferably bondedtogether along at least a portion of their abutting surfaces to form alaminate wherein the stabilizer element is in contact with and bonded toboth the first sheet member and, where present, the second outer sheetmember. It is desirable, although not required, that the bond be formedalong at least a portion of a peripheral edge of the barrier member tosubstantially prevent the escape of any of the barrier material frombetween the first and second outer sheet members.

The nature of the stabilizer element in which the selectivelyfluid-impermeable barrier material is deposited is determined by thenature of the impermeable material which is to be contained therein. Forexample, the stabilizer element could be either a geogrid or a geonet,as those terms are defined below, in a waste containment facility liner,wherein the element is preferably formed from a polymeric plastic. Inalternate arrangements, however, the stabilizer element could be formedof a textile, wire mesh, honeycomb material or in any shape orconfiguration which is capable of preventing movement of the impermeablematerial and which can be bonded to the outer sheet member. Thestabilizer element also provides increased bearing capacity to thebarrier material and prevents the selectively fluid-impervient materialfrom being squeezed out when, for example, waste material orconstruction equipment is placed above it.

In one embodiment of the invention, the stabilizer element is providedwith stop rails formed integrally upon the element's surface. The stoprails facilitate prevention of sliding movement of the selectivelyfluid-impervient barrier material, e.g., when the barrier member isinstalled upon a surface which is not substantially horizontal, bycreating an additional physical barrier to the movement of thefluid-impervient material and by providing additional surface area forbonding the stabilizer element with the first and (optional) secondouter sheet members. A stabilizer element constructed as defined abovealso increases the shear and tensile resistance of a barrier memberformed therewith.

In a still further embodiment, the invention comprises a stabilizedgeocomposite waste containment facility liner including a first outersheet member having a top surface and a bottom surface. The first sheetmember is formed from a material selected from the group consisting ofgeotextiles and geomembranes. The waste containment facility linerfurther comprises a stabilizer element, such as a geonet or geogrid,which overlays the top surface of the first outer sheet member and abutsthe top surface along at least a portion thereof. The preferredstabilizer elements for use in constructing the liner are formed from apolymeric plastic.

The stabilizer element contains a plurality of interstitial aperturesadapted for containing a water swellable colloidal clay and forsubstantially preventing displacement of the clay from the apertures,notwithstanding the angular inclination at which the liner is oriented.The water-soluble clay minerals preferred for use with the invention areselected from the group consisting of attapulgite, brucite, chlorite,gibbsite, halloysite, illite, kaolinite, montmorillonite, vermiculiteand the like.

The waste containment facility liner may, as noted above, optionallycomprise a second outer sheet member, also formed from a materialselected from the group consisting of geotextiles and geomembranes. Thesecond outer sheet member has a top surface and a bottom surface and,when included, is positioned so as to overlie the stabilizer elementsuch that at least a portion of the second sheet member bottom surfaceabuts the stabilizer element.

Upon stacking the components in abutting relation they are all bondedtogether along at least a portion of their abutting surfaces to form abonded laminate in which the stabilizer element is in contact with andbonded to at least a portion of the first sheet member and, optionally,the second outer sheet member.

In one embodiment of the geocomposite waste containment facility linerdescribed above, the first and/or second outer sheet members are formedfrom geotextiles. One preferred geotextile is non-woven polyester. Inanother embodiment, the first and/or second outer sheet members aregeomembranes. A preferred geomembrane for use in forming thegeocomposite waste containment facility liner of the invention ispolyethylene.

A still further embodiment of the invention concerns a method forforming a stabilized fluid barrier member, which method comprises, in afirst step, providing a first outer sheet member formed from a materialselected from the group consisting of geotextiles and geomembranes. Thefirst outer sheet member has a top surface and a bottom surface.

A further step in forming the barrier member of the invention involvespositioning, upon the top surface of the first sheet member and inabutting relation with at least a portion of the first outer sheetmember top surface, a stabilizer element containing within the element aplurality of interstitial apertures adapted to contain a selectivelyfluid-impervient barrier material and to substantially preventdisplacement of the barrier material from the apertures, notwithstandingthe angular inclination at which the fluid barrier member is orientedduring manufacture, transport, installation, and/or use. Theinterstitial apertures formed by the stabilizer element are at leastpartially filled with one or more selectively fluid-impervient barriermaterials. Various fluid-barrier materials may be deposited within theinterstitial apertures, either singly or in combination, depending uponwhich fluid(s) is/are to be barred from passage in a particularapplication.

Thereafter, a second outer sheet member may optionally be positioned ontop of the stabilizer element. The optional second sheet member also hasa top surface and a bottom surface and is formed; as is the firstmember, from a material selected from the group consisting ofgeotextiles and geomembranes. The second sheet member, when included, ispositioned atop the stabilizer element in a manner such that at least aportion of the second sheet member bottom surface is in abuttingrelation with an upper surface of the stabilizer element. Subsequently,the first and, where present, the second outer sheet members and thestabilizer element are all bonded together along at least a portion oftheir abutting surfaces to form a laminated fluid barrier member whereinthe stabilizer element is in contact with and bonded to at least aportion of the first outer sheet member and, where present, the secondouter sheet member. Where the optional second sheet member is notincluded, an adhesive may be used, if desired, to retain the barriermaterial within the apertures in the stabilizer element.

In an alternate embodiment, the barrier material is placed on a surfaceand a unitary construct, comprising a stabilizer element formed integralwith or bonded to an outer sheet member is placed over the material suchthat the apertures in the stabilizer element are filled with the barriermaterial. The dirt overlying the barrier member retains the barriermaterial in the stabilizer element.

Alternately, in a still further embodiment, the unitary constructdescribed above may simply be positioned at the job site, whereupon thestabilizer element is filled with one or more fluid impervient materialsand the resultant barrier member is covered with, e.g., soil or sand.Prior to burying the barrier member described above, i.e., having onlyone outer sheet member, under soil or sand, it may in some instances bedesirable to, for example, deposit a protective layer across the exposedsurface of the barrier material, e.g., to hinder the passage of moisturefrom the surrounding soil directly into the barrier material.

The bonding operation may be carried out using a variety of methods wellknown in the art. Preferably, bonding is achieved by a method selectedfrom heat bonding, infrared welding, ultrasonic welding, adhesivebonding and combinations thereof. As noted above, it is desirable,although not required, to form the bond along a peripheral edge portionof the barrier member components to substantially prevent the barriermaterial from escaping from in between the first and second outer sheetmembers and preventing shear failure through the liner after hydration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a representativeunstrengthened prior art geosynthetic clay waste containment facilityliner;

FIG. 2 is a sectional view through a representative prior artstrengthened geosynthetic clay waste containment facility liner;

FIG. 3 is an exploded perspective view of one embodiment of a stabilizedfluid barrier member formed according to the present inventioncomprising two outer sheet members;

FIGS. 3A and 3B are partial perspective views illustrating alternateconfigurations of the geogrid stabilizer element shown in FIG. 3;

FIG. 4 is an exploded perspective view of an alternate embodiment of astabilized fluid barrier member formed according to the invention;

FIG. 5 is an exploded perspective view of another alternate embodimentof a stabilized fluid barrier member formed according to the invention;and

FIG. 6 is a partial plan view illustrating several stop rails upon thesurface of a stabilizer element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning initially to FIG. 1 there is illustrated a typical example of anunstrengthened geosynthetic clay waste containment facility liner("GCL") 10. GCL 10 generally comprises a first sheet 12 and a secondsheet 14 of geosynthetic material sandwiching a layer of awater-swellable colloidal clay 16, which is typically bentonite. Asillustrated, the geosynthetic material used in forming the GCL is ageotextile, but geomembranes are also used in place of the geotextilesfor specific applications. Geotextiles most commonly used in formingsuch GCLs include woven and non-woven polyesters. A commonly usedgeomembrane is high density polyethylene ("HDPE"). Original GCLs, of thetype illustrated in FIG. 1, are typically held together with the use ofglue or some other type of adhesive.

As used herein, the term "geosynthetic" relates generically to allsynthetic materials used in geotechnical engineering applications.Moreover, the term "geotextile" is herein defined to include anypermeable or non-permeable textile used with foundation, soil, rock,earth or any other geotechnical engineering related material as anintegral part of a man-made project, structure or system. A"geomembrane", on the other hand, is defined as an essentiallyimpermeable membrane used as a liquid or vapor barrier in any of theapplications described above with regard to geotextiles.

FIG. 2 illustrates the general appearance of a typical prior artstrengthened GCL 20. Strengthened GCL 20 is similar in many respects toGCL 10 in that it comprises a layer of water-soluble colloidal clay 22,e.g., bentonite, sandwiched between two geotextile sheets 24, 26, oralternately, encompassed by one or two geomembranes (not shown). Instrengthened GCL 20, the two geotextile sheets 24, 26 are joined byneedle punching a plurality of, e.g., polyester or polypropylene fibers28, from one geotextile through the other geotextile and the interveningbentonite layer in a mechanical bonding process using barbed needles.The fibers 28 may be secured, for example, by anchoring them with africtional connection, i.e., wherein they become tangled with the fibersof the geotextile. The bond provided by fibers 28 serves a two-foldpurpose, i.e., (1) to hold the GCL together during handling anddeployment and (2) to provide increased in-plane shear strength afterdeployment.

In the field, GCLs of the type illustrated in FIGS. 1 and 2 areself-sealing at the overlaps between panels (see, e.g., Estornell, P.and Daniel, D. E., Journal of Geotechnical Engineering, Vol. 118, No.10, October, 1992, pp. 1592-1606). That is, when water hydrates the clayin the GCL, the clay swells and automatically seals the overlap. Ifdesired, however, a small amount of loose granular bentonite can beplaced between the panels at the point of overlap to assist inself-sealing upon hydration.

Turning now to FIG. 3, there is illustrated one embodiment of thestabilized fluid barrier member 30 of the present invention. Barriermember 30 is comprised of a first outer sheet member 32 having a topsurface 34 and a bottom surface 36. Overlaying at least a portion of topsurface 34, preferably the entire top surface of sheet 32, is stabilizerelement 38. Stabilizer element 38 abuts top surface 34 of first sheet 32along at least a portion of the top surface. Stabilizer element 38contains a plurality of interstitial apertures 40. Apertures 40 areadapted to contain a quantity of one or more selectivelyfluid-impervient barrier materials 42 and for substantially preventingdisplacement of material(s) 42 within barrier member 30, notwithstandingthe angular orientation at which barrier member 30 is oriented duringmanufacture, storage, transport, installation or while in use.

The barrier member 30 of the invention may additionally comprise, ifdesired, an optional second outer sheet member 44 having a top surface46 and a bottom surface 48. Second sheet member 44, when included,overlies at least part of the stabilizer element 38 and preferablycovers the entire element 38. One advantage of forming a barrier member30 without a second (i.e., upper) outer sheet member is that such aconstruction has an enhanced shear resistance due to the interlock whichoccurs between the stabilizer element which contains the barriermaterial and the soil underlying or overlying member 30. The interlockoccurs due to the weight of this soil against barrier member 30. Inaddition, the pressure of this soil keeps the barrier material fromexiting the apertures in the stabilizer element, even when member 30 isinstalled upon a sloped surface.

After the various components 32, 38, 42, 44 (optional) of barrier member30 are arranged in stacked relation, they are all bonded together alongat least a portion of their abutting surfaces to form a laminate whereinstabilizer element 38 is in contact with and bonded together with boththe first 32 and second 44 sheet members. Not all the areas which are incontact are necessarily bonded, however. The proportion of the surfacewhich is actually bonded is a matter of discretion, depending upon thestrength of the bond required for a specific application.

First sheet member 32 and (optional) second sheet member 44 are formedfrom either a geotextile or a geomembrane. Preferred geotextiles for usewith the invention include, but are not limited to, woven and nonwovenpolypropylene, polystyrene, polyester polyamide (e.g., nylon),polypropylene-polyethylene copolymers and polypropylene-polyamidecopolymers. The thickness of the textile fabric is not critical and mayrange between about 3-30 mils or 2 to 36 ounces per square yard. Themost preferred geotextile for use in forming the outer sheet members 32,44 is a four to sixteen ounce per square yard nonwoven polyestergeotextile.

Alternately, as noted above, geotextiles may be replaced by geomembranesfor use with the invention. Such geomembranes may be formed, forexample, from materials such as polyolefins, chlorosulfonatedpolyethylenes, silicone rubbers, polyisoprenes, polyesters, polyamides(e.g., nylon), polyvinyl chlorides, flexible polypropylene andpolystyrenes. Preferred polyolefins include but are not limited topolypropylene, polyethylene and polybutylene. Polyethylene is the mostpreferred polyolefin material for use in forming the geomembranes usedin the invention. If desired, for certain applications where barriermember 30 comprises both first 32 and second 44 sheet members, the twosheet members can be formed out of different materials, e.g., whereinone is a geotextile and one is a geomembrane, or wherein they are formedfrom two different geotextiles or two different geomembranes.

Preferred stabilizer elements 38 for use with the invention includegeogrids 38 (shown in FIG. 3) and geonets (see, e.g., FIG. 4), althoughvarious other constructions, such as an entangled mesh (see, e.g., FIG.5 and the discussion thereof below), may be used in the invention. Asused herein, the term "geogrid" means a deformed or nondeformablegridlike polymeric material found by intersecting ribs joined at thejunctions and used to provide increased tensile capacity, reinforcementand bearing capacity. A particularly suitable geogrid for use with thepresent invention is the TENSAR GEOGRID manufactured by the TENSARCorporation located in Morrow, Ga.

FIGS. 3A and 3B illustrate alternate embodiments of the invention inwhich the apertures contained within the geogrid are not substantiallyrectangular as shown in FIG. 3, but instead are, respectively,ellipsoidal and hexagonal in shape. As one of ordinary skill in the artwould recognize, the apertures may be virtually any size and shape andmay be configured in virtually any arrangement. In a preferredembodiment however, apertures 40 are of a minimum size, i.e., at leastabout 0.4 inch by 0.4 inch in plan dimension and 0.2 inch thick. Thepreferred material for forming the geogrids and geonets of the inventionis a polymeric plastic, such as polyethylene and the like. Mostpreferred is high density polyethylene.

Returning to FIG. 3, contained within aperture 40 in stabilizer element38 is a quantity of one or more relatively fluid-impermeable materials,either individually or in admixture. In a preferred embodiment of theinvention, a layer of an adhesive is first sprayed into the emptyapertures to prepare them for the addition of material 42. If desired,material 42 may be added to the apertures in batches with an adhesivelayer being interposed between each (or some) batches. When theapertures are completely filled, a final adhesive layer may be applied(e.g., by spraying) across the upper surface of filled element 38 to"cap" the element, that is, to prevent spillage of material 42 out ofelement 38 when barrier member 30 is angled or tilted. This adhesive isparticularly useful in those applications which do not include a second(i.e., upper) sheet member.

In a further alternate embodiment of the invention, the barrier memberof the invention comprises a first outer sheet member and a stabilizerelement either formed integral with the sheet member or bonded thereto.The apertures in the stabilizer element are substantially filled with atleast one fluid-impervient barrier material, either on-site or at afactory where the barrier member is fabricated. Once the barrier memberis installed at the job site, the uncovered surface of the stabilizerelement is covered by a protective material. This protective materialmay be, for example, a second geomembrane or geotextile sheet which maybe simply laid over the stabilizer element without bonding to thestabilizer element or to the first sheet member. Alternately, forexample, an adhesive or a geomembrane material dissolved in a suitablesolvent could be sprayed onto the filled stabilizer element to form a"cap" or layer thereover. As the solvent evaporates, the adhesive orgeomembrane bonds to the, barrier material, the stabilizer element andoptionally to the first sheet member to protect the underlying materialsby e.g., hindering or substantially blocking the passage of water fromthe surrounding soil once the barrier member is in operation.

In a still further embodiment the barrier material chosen for use withthe invention is a material which undergoes a phase change, e.g., from aliquid or a gel to a solid, upon contact with a particular fluid, thepassage of which the barrier member is intended to block. In a situationwhere the barrier member has only one outer sheet member bonded orformed integrally with the stabilizer element, a second protectivelayer, e.g., a geotextile or geomembrane sheet, can be laid over theexposed surface of the filled stabilizer element, in contact with thebarrier material in the apertures of the stabilizer element, withoutbonding the second protective sheet to any portion of the barriermember. Thereafter, when the barrier material undergoes a phase change,i.e., when it solidifies from a liquid or a gel to a solid, the secondsheet member is effectively bonded to the barrier member by being"captured" by the solidified barrier material.

Possible fluid-impermeable materials for use with the invention include,but are not limited to the man-made materials known in the art as"superabsorbent" polymer resin materials and, in addition, naturallyoccurring materials such as, sand, starch, e.g., corn starch and theswellable colloidal clay minerals. For a discussion and description ofvarious superabsorbent polymer resins see, e.g., Askari, et al.,"Synthesis and Characterization of Acrylic-Based Superabsorbents",Journal of Applied Polymer Science, Vol. 50, No. 10, Dec. 10, 1993, pp.1851-1855, the disclosure of which is incorporated herein by reference.As noted above, a wide variety of additional natural and man-madematerials may be chosen for use as the barrier material depending uponthe proposed application for the barrier member and the invention is notlimited to use with the specific examples which are provided above.

In preferred embodiments of the invention, the superabsorbent polymerresins and/or the colloidal clays may be used in either their dry orhydrated form, with any degree of water content. Preferredsuperabsorbent polymer resins for use in the invention includepolyacrylic acid/polyalcohol grafted copolymers, polyacrylatehomopolymers, polyacrylate/polyalcohol copolymers,polyacrylate/polyacrylamide terpolymers, polyacrylonitriles, andpolyacrylate, acrylamide and cross-linked polyacrylic acid. A preferrednatural absorbent is starch, e.g., corn starch.

Suitable superabsorbents include those sold under the trade namesDynasorb-Terrasafe, Dynasorb-Aquasafe, Dynasorb-PestiSafe andDynasorb-Acidsafe, all of which are manufactured by Stockhausen Inc.located in Greensboro, N.C. The "Acidsafe" product is used to barpassage of acids, including sulfuric acid, boric acid, acetic acid,nitric acid, hydrochloric acid, phosphoric acid and the like, whereasthe "Aquasafe" and "Terrasafe" products are useful in barring passageof, for example, materials such as oil, diesel fuel, jet fuel, paints,lacquers, thinners, gasoline, citrus oil and transmission fluid.

As noted above, one use for the fluid barrier member 30 of the inventionis in forming a geosynthetic clay liner for use in waste containmentfacilities. In such products, the fluid-impermeable material 42 ofchoice is a water-swellable colloidal clay mineral. Preferred clayminerals include attapulgite, brucite, chlorite, gibbsite, halloysite,illite, kaolinite, montmorillonite, vermiculite and the like. By far,the most preferred of these is granulated sodium bentonite, amontmorillonite clay.

The clay is most preferably deposited within the apertures in thestabilizer element at the rate of about one pound per square foot of theliner. Since the invention uses substantially the same amount of clay asis found in prior art GCLs, the barrier member 30 of the inventionprovides similar or even reduced hydraulic conductivities, i.e., withinthe required range, to those achieved in the prior art products.

The lower hydraulic conductivity values obtainable with the inventionresult from the stabilizer element confining lateral expansion of thebentonite and the first and second sheet members resisting verticalexpansion thereof. The resistance to expansion results in a tighterpacking of the bentonite and a lower value of hydraulic conductivitythan is found in existing GCL products.

Some physical characteristics which distinguish bentonite from otherclays are its permeable texture and its extremely small grain size. Thestrong absorptive power of commercial bentonite, which will absorbalmost 5 times its weight of water, is partially attributable to thepreponderance of extremely small grains or particles, providingtremendous surface area for the exertion of absorptive powers and thefilm retaining capacity of these particles.

The bentonite granules for use with the present invention preferablyrange in size from that capable of passing through a 200 mesh U.S.Standard Sieve (0.003 inch grain diameter) upwards to about 3/16 to 5/16of an inch, most preferably between about 0.003 to about 1/4 inch. Thegrain particles, when wetted, absorb films of water that are thickerthan the films which form on other clay-like materials, and after thebentonite has been wetted the water cannot be expelled, even at highpressures. An important aspect of the swelling of bentonite is that itwill swell to the extent necessary to fill available space and exertpressure when confined against further swelling. This leads to lowervalues of hydraulic conductivity than existing GCL products because thestabilizer element does not allow unrestrained swell.

The various components of the stabilized fluid barrier member 30 of theinvention are therefore stacked and then laminated by bonding them alltogether along at least a portion of their abutting surfaces. The bondis preferably formed along an outer peripheral edge portion of the stackto prevent leakage of the selectively fluid-impervient material frommember 30. Alternately, or in addition, however, member 30 may also bebonded together at points within the laminate located inwardly from theperipheral edge. For this purpose, the stabilizer element may beprovided with stop rails (discussed below with regard to FIG. 6) whichact as a further barrier to sliding movement of the barrier material andwhich, in addition, provide additional surface area for attaching thefirst and second outer sheet members 32, 44 to the stabilizer element38, thus strengthening the bond among these components.

In an alternate embodiment of the method of making barrier member 30, acombination geomembrane or geotextile/geogrid or geonet is extruded orotherwise manufactured as a unitary construct, i.e., as a singlecomponent. This construct may then be transported directly to the sitewhere it is desired to form a barrier, and installed in place.Thereafter, the apertures in the geonet or geogrid are filled with oneor more barrier materials, thus creating barrier member 30. In analternate embodiment, if desired, a second (optional) geotextile orgeomembrane may be laid atop the barrier material,.or even bondedthereto, e.g., to protect against loss or oversaturation of the barriermaterial in areas of high humidity or precipitation and unrestrainedswell.

The thickness of a geosynthetic clay liner produced as discussed aboveranges between about one-quarter inch to two inches. The cost ofproduction is approximately 50¢/ft² -$1.50/ft², i.e., only slightly moreexpensive than the strengthened GCLs of the prior art.

Bonding of the laminate components can be carried out by a variety ofmethods well known in the art. The preferred methods include adhesivebonding, ultrasonic welding, infrared welding and most preferably, heatbonding, or combinations of the above methods. The heat bonding processis carried out, as would be well known in the art, by at least partiallymelting the plastic geonet or geogrid by the application of thermalenergy and applying pressure to force a portion of the geotextile(s) orgeomembrane(s), into the melted material so as to form a plurality of"weld points" between the first and optionally, the second outer sheet(i.e., geotextile or geomembrane) and the stabilizer element. The amountand duration of the thermal treatment and the number and location ofweld points may be varied as necessary, depending upon the strengthdesired for the bond and the intended application for the finishedproduct.

In an additional embodiment of the invention, to facilitate manufacturethe stabilizer element and a geomembrane or a geotextile forming thefirst outer sheet member are manufactured as a single, integratedcomponent as described above, thus obviating the necessity of bondingthem together later on. This method is especially cost effective andtime saving in those applications which do not require a second outersheet since one thus need only, for example, extrude a combinationgeomembrane or geotextile/geogrid or geonet as described above and thenpack the grid or net with barrier material.

Heat bonding as described above results in high peak and residualinternal strengths by preventing shear failure through the bentonite. Inaddition, it prevents damage to the barrier member 30 during swelling ofthe fluid-impervient material, e.g., bentonite, during hydration andprevents material failure of the member 30 due to shear forces. Suchswelling will not burst the bonds, particularly thermal bonds, such asmay be used in the present invention in contrast to prior art productswherein swelling of the bentonite upon hydration has been known to tearor pull out the vertical stitching connecting the geotextiles.

FIG. 4 illustrates a barrier member constructed according to theinvention which is in many respects identical to that illustrated inFIG. 3. For this reason, the same numbers have been used to identifysimilar structural elements in FIGS. 3 and 4. One difference, however,between the barrier member 30 shown in FIG. 3 versus that illustrated inFIG. 4 is that the stabilizer element 50 in FIG. 4 is a geonet, not ageogrid. A "geonet" is defined as a netlike polymeric material formedfrom intersecting ribs integrally joined at the junctions. As can beseen from FIG. 4, the geonet 50 presents a different, i.e., woven,appearance than the geogrid, i.e., the apertures 52 among the wovenstrands are less regular in appearance. In a manner similar to thatshown in FIG. 3, the selectively fluid-impermeable material 42 in theembodiment shown in FIG. 4 is deposited within the apertures 52 of thegeonet 50 and is thus prevented from being substantially displacedwithin barrier member 30, not withstanding the angular orientation ofmember 30. The preferred material for forming the geonets of theinvention is a polymeric plastic such as polyethylene and the like. Mostpreferred is high density polyethylene.

FIG. 5 illustrates still another embodiment of a barrier memberconstructed according to the invention. As above, it is in many respectssimilar to the constructions shown in FIGS. 3 and 4 and thus similarstructures are again numbered alike. FIG. 5 illustrates the use of anentangled mesh 54 as the stabilizer element. The selectivelyfluid-impermeable material 42 is deposited within the apertures 56defined by the entangled mesh 54 and are thus prevented from becomingdisplaced when the barrier member is tilted, rotated or otherwise movedout of a substantially horizontal plane, e.g., during manufacture,transport and/or use.

FIG. 6 illustrates a stop rail 58 formed integrally on the surface of,for example, the geonet stabilizer element shown in FIG. 3. A geonet 50is shown in FIG. 5 for purposes of illustrating the stop rails used inthe invention, but the use of stop rails is not limited to geonets,i.e., they can also be formed upon geogrids as well as otherconstructions used to form the stabilizer element. By increasing thewidth of one rail or filling in a row of apertures, any fluid-impervientmaterial which does manage to escape from aperture 52 does not allcollect in one location. Rather it is scattered in all directions,preventing the build-up of excessive shear which may otherwise damagethe barrier member. As can be seen from FIG. 6, the stop rails 58 arerails which are built up in height or width to that of the adjacentrails to prevent, as much as possible, shifting of material 42 out ofapertures 52. An additional beneficial effect of rails 58 is that theyincrease the bonding area between the stabilizer element and thegeotextile or geomembrane in those applications when barrier member 30comprises such a second sheet member.

In one embodiment of the invention, the stop rails 58 are located alongthe outer peripheral edges of the stabilizer member, adjacent the outeredges of the laminate. The invention is not limited to thisconfiguration, however, as any desired number of stop rails may beemployed at any desired location(s) upon the stabilizer element. Thenumber and spacing of these rails is a function of several factors,i.e., the nature of the stabilizer element, the angle at which thebarrier member of the invention is to be installed, the relativecoarseness or fineness of the fluid-impervient materials chosen for usewith the invention, and the shear resistance required to prevent failurethrough the impervient material.

As would be well recognized by one of ordinary skill in this art, theinvention described and illustrated herein is capable of a variety ofmodifications. All such modifications falling within the spirit andscope of the appended claims are believed to form part of applicant'sinvention.

I claim:
 1. A stabilized containment facility liner, comprising:a firstouter sheet member having a top surface and a bottom surface; astabilizer element overlying at least part of the top surface of saidfirst sheet member and abutting said top surface along at least aportion thereof, said stabilizer element having a plurality ofinterstitial apertures adapted to contain a selectively fluid-impervientbarrier material and for substantially preventing said barrier materialfrom flowing out of said liner, notwithstanding the angular inclinationat which said liner is oriented; and at least one selectivelyfluid-impervient barrier material contained within the interstitialapertures of said stabilizer element, wherein said first sheet memberand said stabilizer element are bonded together along at least a portionof their abutting surfaces to form a laminate having a sufficienttensile resistance and shear strength to maintain stability of saidliner upon a sloped surface and sufficient compressive strength toprevent any substantial change in liner thickness after manufacturethereof, wherein the stabilizer element is in contact with and bonded toat least a portion of said first outer sheet member.
 2. The liner ofclaim 1 which further comprises an adhesive, said adhesive applied to atleast said stabilizer element to facilitate retaining said selectivelyfluid-impervient barrier material within the apertures of saidstabilizer element notwithstanding the angular inclination at which saidliner is oriented.
 3. The liner of claim 1 which further comprises asecond outer sheet member, said second outer sheet member having a topsurface and a bottom surface and overlying at least part of saidstabilizer element such that at least a portion of said second sheetmember bottom surface abuts said stabilizer element.
 4. The liner ofclaim 3 wherein said first and said second outer sheet members are eachformed of a material selected from the group consisting of geotextilesand geomembranes.
 5. The liner of claim 4 wherein at least one of saidfirst and said second outer sheet members are formed from a geotextileselected from the group consisting of woven and nonwoven polypropylene,polystyrene, polyester, polyamide, polypropylene-polyethylene copolymersand polypropylene-polyamide copolymers.
 6. The liner of claim 5 whereinsaid first and said second outer sheet members are geotextiles comprisedof a nonwoven polyester.
 7. The liner of claim 4 wherein at least one ofsaid first and said second outer sheet members is formed from ageomembrane selected from the group consisting of polyolefins,chlorosulfonated polyethylenes, silicone rubber, polyisoprene,polyester, polyamide, polyvinyl chloride and polystyrene.
 8. The linerof claim 7 wherein the geomembrane is formed from a polyolefin selectedfrom the group consisting of polypropylene, polyethylene andpolybutylene.
 9. The liner of claim 8 wherein said first and said secondouter sheet members are geomembranes formed of polyethylene.
 10. Theliner of claim 1 wherein said stabilizer element is a geonet or ageogrid.
 11. The liner of claim 1 wherein said stabilizer element isformed from a polymeric plastic.
 12. The liner of claim 11 wherein saidpolymeric plastic is selected from the group consisting ofpolypropylene, polyethylene, polybutylene, polyester, polyamide,polyvinyl chloride and polystyrene.
 13. The liner of claim 1 whereinsaid selectively fluid-impervient barrier material is selected from thegroup consisting of superabsorbent polymer resins, sand, starches andwater-swellable colloidal clay minerals.
 14. The liner of claim 13wherein said superabsorbent polymer resin is selected from the groupconsisting of polyacrylonitrile, polyacrylic acid/polyalcohol graftedcopolymers, polyacrylate homopolymers, polyacrylate/polyalcoholcopolymers, polyacrylate/polyacrylamide terpolymers and polyacrylate,acrylamide, and cross-linked polyacrylic acid.
 15. The liner of claim 13wherein said water-swellable colloidal clay mineral is selected from thegroup consisting of attapulgite, brucite, chlorite, gibbsite,halloysite, illite, kaolinite, montmorillonite and vermiculite.
 16. Theliner of claim 15 wherein said water-swellable colloidal clay isbentonite.
 17. A stabilized containment facility liner comprising:afirst outer sheet member formed from a material selected from the groupconsisting of geotextiles and geomembranes, said first sheet memberhaving a top surface and a bottom surface; a stabilizer elementoverlying at least part of the top surface of said first outer sheetmember and abutting said top surface along at least a portion thereof,said stabilizer element having a plurality of interstitial aperturesadapted to contain a selectively fluid-impervient barrier material andfor substantially preventing said barrier material from flowing out ofsaid liner, notwithstanding the angular inclination at which said lineris oriented; a second outer sheet member formed from a material selectedfrom the group consisting of geotextiles and geomembranes, said secondsheet member having a top surface and a bottom surface, wherein saidsecond sheet member overlies at least part of said stabilizer elementsuch that at least a portion of said second sheet member bottom surfaceabuts said stabilizer element; and at least one selectivelyfluid-impervient barrier material contained within the interstitialapertures of said stabilizer element; wherein said first sheet member,said stabilizer element and said second sheet member are bonded togetheralong at least a portion of their abutting surfaces to form a laminatehaving a sufficient tensile resistance and shear strength to maintainstability of said liner upon a sloped surface and sufficient compressivestrength to prevent any substantial change in liner thickness aftermanufacture thereof wherein the stabilizer element is in contact withand bonded to at least a portion of said first and said second outersheet members.
 18. The liner of claim 17 wherein at least one of saidfirst and said second outer sheet members is formed from a geotextileselected from the group consisting of woven and nonwoven polypropylene,polystyrene, polyester, polyamide, polypropylene-polyethylene copolymersand polypropylene-polyamide copolymers.
 19. The liner of claim 17wherein at least one of said first and said second outer sheet membersis formed from a geomembrane selected from the group consisting ofpolyolefins, chlorosulfonated polyethylenes, silicone rubber,polyisoprene, polyester, polyamide, polyvinyl chloride and polystyrene.20. The liner of claim 17 wherein said selectively fluid-impervientbarrier material is selected from the group consisting of superabsorbentpolymer resins, sand, starches and water-swellable colloidal clayminerals.
 21. The liner of claim 17 wherein said stabilizer element isformed from a polymeric plastic.
 22. The liner of claim 17 which furthercomprises one or more stop rails formed integrally with an outer surfaceof the stabilizer element, wherein said stop rails facilitate preventionof sliding movement by said selectively fluid-impervient barriermaterial by providing additional surface area for bonding saidstabilizer element with said first and said second outer sheet members.